Chapter 9 Flashcards
What is PAO2?
Alveolar partial pressure
How is PAO2 calculated?
PAO2 = FiO2 (barometric pressure - saturated pressure of water) - PaCo2/0.8
What is the normal alveolar-arterial oxygen gradient?
Room air - <25
100% oxygen - <120
How is BE calculated? What is it’s advantage over HCO3?
The amount of acid needed to to return pH to 7.4 at PaCO2 of 40
Takes into consideration all buffering systems, not just H2CO3-HCO3 buffer
What is normal BE?
+/-4
Ddx metabolic acidosis
Loss of HCO3 - d+
Failure to excrete H+ - RTA
Acid accumulation - lactic (shock), DKA
How is anion gap calculated?
AG = (Na + K) - (Cl + HCO3)
What is normal anion gap?
Dogs - 12-25
Cats - 13-27
What is the physiological cause of a normal anion gap acidosis?
Decrease in HCO3 balanced by increase in chloride or unmeasured anions
What causes high anion gap acidosis?
D - hyperosmolar non-ketotic DM, DKA
U - uraemia/azotaemia
E - ethylene glycol (also aspirin, methanol, paraldehyde)
L - lactic acidosis
What causes normal anion gap acidosis?
D+
Early renal failure
RTA
Carbonic anhydrase inhibitor
Acidifying agents
Hyperalimentation
Rapid IV rehydration (dilution of HCO3)
Ketoacidosis with renal ketone loss
What causes a low anion gap?
Retained non-sodium cations (hyperproteinaemia, ^^Ca++, ^^Mg, lithium toxicity) => extracellular fluid Na reduced to maintain electroneutrality
Hypoalbuminaemia, dilution - dilutes unmeasured anions, compensatory increase in anions to maintain electroneutrality
Not normally associated with acidosis
Ddx metabolic alkalosis
HCO3 overload
Severe gastric vomiting
Loop/thiazide diuretics
Acute respiratory acidosis - what is the expected compensation for each 10mmHg increase in PaCO2?
^HCO3 by 1.5
Chronic respiratory acidosis - what is the expected compensation for each 10mmHg increase in PaCO2?
^HCO3 by 3.5
